1. Field of the Invention
The present invention relates generally to methods and medical devices that gather information about vessels, structures or devices in a body and more particularly to methods and medical devices for measuring dimensions of such vessels, structures or devices and calculate cross-sectional areas of such vessels, structures or devices.
2. Description of Related Art
Within the field of interventional cardiology, the utilization of coronary drug-eluting stents has significantly reduced stent failure and the need for revascularization. Recent imaging studies have illustrated that the predominate cause of residual stent failure is stent underexpansion and lesion edge problems such as undersizing the length of the stent needed to appropriately cover the lesion. The limitations of today's angiogram often do not allow the physician to adequately assess the lesion prior to stent placement or determine the degree of expansion of the deployed stent. This is a problem in need of a solution.
Current imaging catheters utilize ultrasound or optical technologies to provide a cross-section image that is then interpreted by the physician to determine, among other characteristics, the dimensions of the lumen surrounding the catheter. For example,
Intravascular Ultrasound (IVUS) is commonly used in interventional diagnostic procedures to image blood vessels to locate and characterize atherosclerosis and other vessel diseases and defects. In use, a guidewire is placed in a vessel of interest. Then, an IVUS catheter is threaded over the guidewire and ultrasonic signals are sent from the catheter, bounced off the tissue, received by the catheter and passed from the catheter to a system. These ultrasound echoes are processed by the system to produce images of the vessel and its physiology.
Optical Coherence Tomography (OCT) systems are also used in interventional diagnostic procedures to image blood vessels to locate and characterize atherosclerosis and other vessel diseases and defects. In use, again a guidewire is placed in a vessel of interest. Then, an OCT catheter is threaded over the guidewire and light signals are sent from the catheter, bounced off the tissue, received by the catheter and passed from the catheter to a system. These light echoes are processed by the system to produce images of the vessel and its physiology.
These IVUS and OCT images and the information about the vessel, including vessel dimensions, is considerably more detailed than the information that is obtainable from traditional angiography images that which shows only a two-dimensional shadow of the vessel lumen. Examples of some of the information provided by IVUS or OCT systems include: determining a diameter of a vessel to be used in determining the correct diameter or a stent to be placed; determining the length of a physiological problem such as the presence of atherosclerotic material so that the correct length of a stent to be placed can be determined to dilate the stenosis; verifying that a stent, once placed, is well apposed against a vessel wall to minimize thrombosis and optimize drug delivery (in the case of a drug eluting stent); verifying that after a stent has been place, the diameter and luminal cross-section area of the stented vessel are adequate; and identifying an exact location of side-branch vessels to aid in stent placement or therapy delivery.
But, although current IVUS and OCT systems provide additional and more detailed information compared to angiograms, these IVUS and OCT systems introduce significant additional time, cost and complexity into minimally-invasive procedures. Further, the images produces by IVUS and OCT systems often are subject to interpretation of the physician. Thus, there is a need for an improved way to get information about a vessel or structure, particularly information about the diameter of a vessel or structure.